On the motion under focal attraction in a rotating medium

New results are established here on the phase portraits and bifurcations of the kinematic model in system (1), first presented by H.K. Wilson in [3], and by him attributed to L. Markus (unpublished). A new, self-sufficient, study which extends that of [3] and allows an essential conclusion for the applicability of the model is reported here.

Radical acetylation of 2`-deoxyguanosine and L-histidine coupled to the reaction of diacetyl with peroxynitrite in aerated medium

Diacetyl, like other alpha-dicarbonyl compounds, is reportedly cytotoxic and genotoxic. A food and cigarette contaminant, it is related with alcohol hepatotoxicity and lung disease. Peroxynitrite is a potent oxidant formed in vivo by the diffusion-controlled reaction of the superoxide radical anion with nitric oxide, which is able to form adducts with carbon dioxide and carbonyl compounds. Here, we investigate the nucleophilic addition of peroxynitrite to diacetyl forming acetyl radicals, whose reaction with molecular oxygen leads to acetate. Peroxynitrite is shown to react with diacetyl in phosphate buffer (bell-shaped pH profile with maximum at 7.2) at a very high rate constant (k(2) = 1.0 X 10(4) M-1 s(-1)) when compared with monocarbonyl substrates (k(2) < 10(3) M-1 s(-1)). Phosphate ions (100-500 MM) do not affect the rate of spontaneous peroxynitrite decay, but the H2PO4- anion catalyzes the nucleophilic addition of the peroxynitrite anion to diacetyl. The intermediacy of acetyl radicals is suggested by a three-line spectrum (a(N) = a(H) = 0.83 mT) obtained by EPR spin trapping of the reaction mixture with 2-methyl-2-nitrosopropane. The peroxynitrite reaction is accompanied by concentration-dependent oxygen uptake. Stoichiometric amounts of acetate from millimolar amounts of peroxynitrite and diacetyl were obtained under nonlimiting conditions of dissolved oxygen. In the presence of either L-histidine or 2`-deoxyguanosine, the peroxynitrite/diacetyl system afforded the corresponding acetylated molecules identified by HPLC-MS"". These studies provide evidence that the peroxynitrite/diacetyl reaction yields acetyl radicals and raise the hypothesis that protein and DNA nonenzymatic acetylation may occur in cells and be implicated in aging and metabolic disorders in which oxygen and nitrogen reactive species are putatively involved.

New material for orthopedic implants: Electrochemical study of nickel free P558 stainless steel in minimum essential medium

Nickel, a component of stainless steels (SS) applied in orthopedic implants may cause allergic processes in human tissues P558 nickel free SS was studied to verify its viability as a substitute for stainless steel containing nickel Its performance is compared to ISO 5832-9 and F138 most used nowadays grades in implants fabrications, in minimum essential medium. MEM, at 37 degrees C. Potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and ""in vitro"" cytotoxicity were used as techniques. From the electrochemical point of view P558 SS is comparable to ISO 5832-9 SS in MEM It remains passivated until the transpassivation potential, above which generalized corrosion occurs F138 presents pitting corrosion at 370 mV/SCE. The cytotoxicity results showed that P558. ISO 5832-9 and F138 do not present cytotoxic character Therefore, these results suggest that P558 SS can be applied in orthopedic implants (C) 2010 Elsevier BV All rights reserved

EVALUATION OF METAL TOXICITY BY A MODIFIED METHOD BASED ON THE FUNGUS GERRONEMA VIRIDILUCENS BIOLUMINESCENCE IN AGAR MEDIUM

Metal cation toxicity to basidiomycete fungi is poorly understood, despite its well-known importance in terrestrial ecosystems. Moreover, there is no reported methodology for the routine evaluation of metal toxicity to basidiomycetes. In the present study, we describe the development of a procedure to assess the acute toxicity of metal cations (Na(+), K(+), Li(+), Ca(2+), Mg(2+), Co(2+), Zn(2+), Ni(2+), Mn(2+), Cd(2+), and Cu(2+)) to the bioluminescent basidiomycete fungus Gerronema viridilucens. The method is based on the decrease in the intensity of bioluminescence resulting from injuries sustained by the fungus mycelium exposed to either essential or nonessential metal toxicants. The assay described herein enables LIS to propose a metal toxicity series to Gerronenia viridilucens based on data obtained from the bioluminescence intensity (median effective concentration [EC50] values) versus metal concentration: Cd(2+) > Cu(2+) > Mn(2+) approximate to Ni(2+) approximate to Co(2+) > Zn(2+) > Mg(2+) > Li(+) > K(+) approximate to Na(+) > Ca(2+), and to shed some li-ht on the mechanism of toxic action of metal cations to basidiomycete fungi. Environ. Toxicol. Chem. 2010;29:320-326. (C) 2009 SETAC

Bismuth Modified Gold Microelectrode for Pb(II) Determination in Wine Using Alkaline Medium

Electrodeposition of bismuth on gold microelectrodes for determination of Pb(II) by square wave anodic stripping voltammetry (SWASV) was accomplished by an in situ procedure in alkaline solution. A linear calibration plot for Pb(II) in the concentration range 40 to 6700 nmol L(-1) (r=0.998) was obtained, the detection limit was found to be 12.5 nmol L(-1) (S/N = 3) and the relative standard deviation in Solutions containing 1 mu mol L(-1) Pb(II) was 4% (n = 12). The analytical performance of the proposed sensor wits tested by measuring the Pb(II) concentration in a wine sample. The result Was in good agreement with the one obtained by GFAAS.

Investigating the formation and the properties of monoalkyl carbonates in aqueous medium using capillary electrophoresis with capacitively coupled contactless conductivity detection

Although alkyl carbonic acids (ACAs) and their salts are referred to as instable species in aqueous medium, we demonstrate that a monoalkyl carbonate (MAC) can in fact be easily formed from bicarbonate and an alcohol even in the presence of a high amount of water. A CE system with two capacitively coupled contactless conductivity detectors (C(4)Ds) was used to obtain different parameters about these species and their reactions. Based on the mobilities obtained for a series of alcohols ranging from 1 to 5 carbons, the coefficients of diffusion and the hydrodynamic radii were calculated. When compared with the equivalent carboxylates, MACs have radii systematically smaller. Although the precise pK(a) values of the ACAs could not be obtained, because of the fast decomposition in acid medium, it was possible, for the first time, to show that they are below 4.0. This result suggests that the acidity of an ACA is quite similar to the first hydrogen of H(2)CO(3). Using a new approach to indirectly calibrate the C(4)D, the kinetic constants and the equilibrium constants of formation were also obtained. The results suggest that the increase in the chain length makes the MACs less stable and more inert.

Ex Situ Scanning Electrochemical Microscopy (SECM) Investigation of Bismuth- and Bismuth/Lead Alloy Film-Modified Gold Electrodes in Alkaline Medium

Scanning electrochemical microscopy (SECM) in feedback mode was employed to characterise the reactivity and microscopic peculiarities of bismuth and bismuth/lead alloys plated onto gold disk substrates in 0.1 molL(-1) NaOH solutions. Methyl viologen was used as redox mediator, while a platinum microelectrode was employed as the SECM tip. The metal films were electrodeposited ex situ from NaOH solutions containing either bismuth ions only or both bismuth and lead ions. Approach curves and SECM images indicated that the metal films were conductive and locally reactive with oxygen to provide Bi(3+) and Pb(2+) ions. The occurrence of the latter chemical reactions was verified by local anodic stripping voltammetry (ASV) at the substrate solution interface by using a mercury-coated platinum SECM tip. The latter types of measurements allowed also verifying that lead was not uniformly distributed onto the bismuth film electrode substrate. These findings were confirmed by scanning electron microscopy images. The surface heterogeneity produced during the metal deposition process, however, did not affect the analytical performance of the bismuth coated gold electrode in anodic stripping voltammetry for the determination of lead in alkaline media, even in aerated aqueous solutions. Under the latter conditions, stripping peak currents proportional to lead concentration with a satisfactory reproducibility (within 5% RSD) were obtained.

Solvatochromism in Binary Mixtures: First Report on a Solvation Free Energy Relationship between Solvent Exchange Equilibrium Constants and the Properties of the Medium

We have employed UV-vis spectroscopy in order to investigate details of the solvation of six solvatochromic indicators, hereafter designated as ""probes"", namely, 2,6-diphenyl-4-(2,4,6-triphenylpyridinium-1-yl) phenolate (RB); 4-[(E)-2-(1-methylpyridinium-4-yl)ethenyl] phenolate, MePM; 1-methylquinolinium-8-olate, QB; 2-bromo-4-[(E)-2-(1-methylpyridinium-4-yl)ethenyl] phenolate, MePMBr, 2,6-dichloro-4-(2,4,6-triphenylpyridinium-1-yl) phenolate (WB); and 2,6-dibromo-4-[(E)-2-(1-methylpyridinium-4-yl)ethenyl] phenolate, MePMBr,, respectively. These can be divided into three pairs, each includes two probes of similar pK(a) in water and different lipophilicity. Solvation has been studied in binary mixtures, BMs, of water, W, with 12 protic organic solvents, S, including mono- and bifunctional alcohols (2-alkoxyethanoles, unsaturated and chlorinated alcohols). Each medium was treated as a mixture of S, W, and a complex solvent, S-W, formed by hydrogen bonding. Values of lambda(max) (of the probe intramolecular charge transfer) were converted into empirical polarity scales, E(T)(probe) in kcal/mol, whose values were correlated with the effective mole fraction of water in the medium, chi w(effective). This correlation furnished three equilibrium constants for the exchange of solvents in the probe solvation shell; phi(W/S) (W substitutes S): phi(S-W/W) (S-W substitutes W), and phi(S-W/S) (S-W substitutes S), respectively. The values of these constants depend on the physicochemical properties of the probe and the medium. We tested, for the first time, the applicability of a new solvation free energy relationship: phi = constant + a alpha(BM) + b beta(BM) + s(pi*(BM) + d delta) + p log P(BM), where a, b, s, and p are regression coefficients alpha(BM), beta(BM), and pi*(BM) are solvatochromic parameters of the BM, delta is a correction term for pi*, and log P is an empirical scale of lipophilicity. Correlations were carried out with two-, three-, and four-medium descriptors. In all cases, three descriptors gave satisfactory correlations; use of four parameters gave only a marginal increase of the goodness of fit. For phi(W/S), the most important descriptor was found to be the lipophilicity of the medium; for phi(S-W/W) and phi(S-W/S), solvent basicity is either statistically relevant or is the most important descriptor. These responses are different from those of E(T)(probe) of many solvatochromic indicators in pure solvents, where the importance of solvent basicity is usually marginal, and can be neglected.